This invention relates to dispensers and more particularly to a selector valve for selection of one of a plurality of fluids for dispensing or mixing with another fluid through a venturi eductor system.
Selector valves of this type typically allow an operator to select and dispense one particular chemical or fluid at a time, while closing off access to all of the other fluid sources available for selection. One such prior selector valve typically included a static body having several inlet ports and one outlet port and a rotatable valve core with passages to allow selective connection of a selected inlet port with the outlet port. Sealing of the non-selected inlet ports was provided by a spring loaded, O-ring sealed plunger carried in the rotatable core and bearing against the face of the static body. While selector valves of this type allow for selective connection and dispensing of a plurality of fluids, they have several inherent disadvantages.
One problem associated with materials typically used in selector valves of this type is the response of the materials to a wide range of temperatures. Selector valves heretofore have been inherently limited to operating environments above a certain temperature due to the limited sealing force supplied by the spring and the propensity for the materials to thermally expand and contract outside of a limited operating temperature. The interference fit and mating relationship between the various components of the selector valve are critically important to the effective sealing of nonselected input fluids. As a result, prior selector valves have been limited to a narrow operating temperature range to avoid thermal expansion and contraction which detrimentally effects the various seals.
Another important aspect of selector valves of this type is the ability to efficiently change over from one selected input chemical or fluid to another. A residual volume of the prior chemical in many systems of this type must be purged prior to inputting a second selected chemical or fluid. Purging the system is very detrimental in that it requires delays in the operation and diminishes the accuracy of the volume and timing of the mixing of the fluids. Because of the distance and the geometry of the path the selected fluid must travel within the selector valve system, the system may contain a significant amount of residual chemical after the user has selected a new inlet port, thereby requiring the user to spend time purging the line.
A contributing factor to the problem of residual fluids in the selector valve is turbulent flow of the fluids through the selector valve. Specifically, the cause of turbulent flow in the selected fluid flow path is commonly stagnation points or blind spots which are typically found at the juncture between mating components. These areas create turbulent flow of the fluid through the selector valve and minimize the ability to effectively purge the valve and flush the residual chemicals. Additionally, turbulent flow through the selector valve retards the fluid flow and requires greater pressures and timing problems for the selected input fluid sources and responsiveness of the selector valve and connected system components.
One solution to some of these identified problems is disclosed in U.S. Pat. No. 5,377,718 which is assigned to the assignee of the present invention and which is hereby expressly incorporated herein by reference. The system of that patent includes a sealing disc with a sealing face biased against an opposed sealing face of a port plate. The sealing disc includes a radially disposed channel located in the sealing face which communicates with an outlet port and a single selected inlet port on the port plate while the sealing disc simultaneously seals off all other inlet ports. A venturi eductor has a suction passage sealed directly to the port plate outlet for connecting the venturi directly to the selected inlet port.
While the system disclosed in U.S. Pat. No. 5,377,718 solved a number of problems associated with prior selector valves, that system was directed to reducing the volume of internal passages within the valve in order to shorten the selected fluid flow path and minimize the residual chemical from a previously selected inlet port when another chemical is chosen. However, the reduction of volume in the internal passages of the selector valve, while providing a successful solution, only addressed one aspect of the problem of residual chemical in the system. The particular geometry of the selected fluid flow path through the selector valve is another contributing factor for residual chemical of fluid. Specifically, crevices between mating components and sharp corners or blind spots in the flow path of the fluid through the selector valve provide areas for the fluid to accumulate even after another fluid has been selected. One such area is a tolerance gap between the selector valve and the eductor to which the valve is connected for fluid flow between these components. This gap is designed into the system to allow for the components to be easily assembled and disassemble as required.
The tolerance gap and other crevices provide potential fluid pathways to crevices between parts and potential areas for leakage of the fluids. Also, the nature and structure of the interface between the port plate of the valve and the eductor plug left certain dead spaces or blind spots in which prior selected chemicals might reside, requiring efficient purge cycles between consecutive fluid selections. Moreover, the selection of a different fluid interrupts flow through the valve and subsequently generates turbulent flow while the crevices and blind spots are filled and flow is not initially at a steady state condition.